CD (compact disk) players have considerably improved in sound quality when compared with conventional LP (long play) record players, and are undergoing further development in order to be superior in the aspect of functional and operational performance. In disks such as CDs, data to be reproduced such as music programs and a variety of control signals are recorded. In accordance with these control signals, a desired music program can be accessed in a short time and the music number and the playback time of the music program can be displayed.
The maximum recording capacity of such a CD is 74 minutes/one side and the spacing between the pits formed on the disk is approximately 1.6 .mu.m. It is virtually impossible to distinguish the music programs when looking at the surface of the disk and hence, the control signals are simultaneously recorded in the CDs with the recording of the signals of music data to be reproduced. The control signal indicates a music number, the playback time of a music program, time elapsed since the start of reproducing the first program stored in the disk, and/or similar information. The music signal pairs with the control signal, and one frame of data is made up of this pair of signals and a synchronizing signal. Such frames are connected in cascade and stored in the recording area of the disk.
The CD player for reproducing music programs from the above disk comprises a PLAY button; a STOP button; ten keys for specifying a program; and a variety of operational buttons for one-touch selection. By operating the operational buttons, a designated position (a music number etc.) is input in order for the optical pick-up to access a desired program. The data input by the operational buttons are read out in the system control circuit and the designated position is stored. Then, the optical pick-up is moved toward the designated position and during this time the pick-up reads the control signals recorded in the disk in order to confirm whether it reaches the designated position. More concretely, each control signal read by the pick-up during the access operation is compared with the designated position, thereby obtaining the distance between the position where the pick-up is at present and the designated position, so that the pick-up is moved as necessary. Thus, the pick-up accesses a desired music program which is stored in the disk, through the above process.
In a LD (laser disk), color video signals and audio signals of 2 channels are recorded. Both video signals and audio signals are recorded in the form of FM (frequency modulation) signals at a constant angular velocity (CAV method) or constant linear velocity (CLV method). When employing the CAV method, a 30 cm LD has a recording capacity of one hour/two sides while a 20 cm LD has a capacity of 28 minutes/two sides. Special reproduction can be easily performed on data recorded with the CAV method.
On the other hand, when employing the CLV method, the recording capacity of a LD is doubled (i.e. a 30 cm LD has a capacity of 2 hours/two sides and a 20 cm LD has a capacity of 40 minutes/two sides). In this case, special reproduction cannot be performed.
In a player used for playing such LDs, a disk is rotated by a motor; a laser beam spot is projected on the recording surface of the disk; a change in the intensity of reflected light therefrom is converted into electric signals by a photodetector; and thereby data are reproduced. Since the frequency elements of signals read from LDs have a broad band-width, the S/N ratio of LDs is high and images obtained therefrom have good resolution compared with standard-type VTRs (video tape recorder).
A plurality of types of CDs and LDs are known which are different in size and multi-disk players capable of solely playing those different disks have been developed. A conventional multi-disk player is provided with a disk mounting section on which a large size disk is placed and another disk mounting section on which a small size disk is placed, these disk mounting sections being disposed in a row. The large size disk mounting section and small size disk mounting section are respectively provided with a driving motor (spindle motor) at the mounting position thereof.
However, in such a conventional player, two driving motors are necessary for playing multiple sizes of disks. That is, a driving motor for playing a large size disk (i.e. a LD) and one for playing a small size disk (i.e. a CD) are required. This results in an increase in the cost as well as the complexity of the circuit structure; besides, there is such a drawback that the whole configuration of the multi-disk player tends to be large and bulky since a large space is occupied by the disk tray.
Some small size disk players (i.e. CD players) are arranged to accommodate a plurality of disks having the same diameter at a time and play a disk selected from them, or successively play the plurality of disks. Such disk players capable of performing the above mentioned selective playing operation/successive playing operation can be used only for small size disks, since the space of the system is limited. Therefore, the development of multi-disk players, which have the capability to play not only small size disks but also large size disks such as laser disks, has been long awaited.